Resilient seat structure



March 5, 1957 A. F. HlcKMAN ETAL 2,783,822

RESILIENT SEAT STRUCTURE Filed April l, 1954 5 Sheets-Sheet 1 March 5,1957 4' A. F. HlcKMAN ErAL 2,783,822

RESTLIENT SEAT STRUCTURE A. F. HlcKMAN ErAL 2,783,822

RESILIENT SEAT STRUCTURE March 5, 1957 5 Sheets-Sheet 3 Filed April l,1954 Q M. KOWJ @www fm ZJ @hm m ff@ ,y J1/Q mmh/9 Qa@ United StatesPatent O RESILIENT SEAT STRUCTURE Albert F. Hickman, Eden, N. Y., andAllison K. Simons, Shorewood, and Charles W. Marcinelr, Milwaukee, Wis.,assignors to Hickman industries, inc., Eden, N. Y., a corporation of NewYork Application April 1, 1954, Serial No. 420,228

9 Claims. (Cl. 15S-50) This invention relates to a seat structure andmore particularly to such a seat structure :designed primarily for usewith extremely rough riding vehicles such as farm tractors and militaryvehicles, features of the seat structure being capable of use inrailroad locomotives and highway trucks. rJl`his application isparticularly an improvement upon the resilient seat suspension describedand claimed in the Albert F. Hickman patent application 279,127, iiledMarch 28, 1952, now Patent No. 2,691,406, granted October l2, 1954,particularly in adapting the important features of said patentapplication to tractor seats, although features of the present inventionare applicable to other types of seat structures.

In common with said Hickman patent application, important objects of thepresent invention are to provide a seat structure, (l) in which the seatpart is permitted to move against a geometric resilient resistance, bothlaterally and vertically, relative to the vehicle on which the seat ismounted; (2) which provides the maximum safety and comfort and leavesthe occupant in full control of all controls of the vehicle; (3) inwhich the seat moves with the occupant and is not drawn or jerked awayfrom the occupant whenever the pressure imposed by the occupant upon theseat becomes negative; (4) which Will operate in a highly desirablefrequency range regardless of the weight of the occupant; (5) which canbe designed, within practical limits, to have any desired frequency andany desired resistance curve; (6) which reduces and cushions both thevertical and lateral impacts against the seated occupant withoutimposing undue thrust on the connections between the seat part and thevehicle; (7) in which torsion springs are employed to provide a longerand a variable spring resistance range; (8) in which the resilientsupport is provided by torsion springs which are simple, compact, low incost and have long life and freedom from service diiculties; (9) inwhich geometric resilient resistance is obtained in a compact structurewhich requires little servicing and is free from noise; (l0) in whichthe load from the seat part to the suspension means and from thesuspension means to its base part is distributed at a plurality ofspaced points; (ll) in which both fore-and-aft and lateral tilting ofthe seat is prevented; (l2) which is made of a plurality of low cost andsturdy sub-assemblies which can be easily coupled together; (13) whichincludes a simple and low cost shackle structure and (14) which isextremely compact and sturdy and which will stand up under conditions ofsevere and constant use with very little servicing.

A specific object of the present invention is to adapt the flexiblebodied connectors forming the subject of the said Hickman patentapplication to a seat for extremely rough riding vehicles, thisadvantageously involving a substantial rearrangement of the parts,location and form of the principal components of the seat structureforming the subject of said Hickman patent application.

Another object of the invention is to provide a simple and efective stopfor limiting particularly the upward movement of the seat part withreference to thebase paru ice of the structure, this stop also beingeffective in determining the pretensioning or so-called windup of therubber torsion springs. A

Another object of the invention is to provide a simple and low costpointer and calibrated scale Which permits the driver to adjust thedegree of pretensioning or windup of the rubber springs to suit hisparticular weight.

Another object of the invention is to provide a rugged and low costmotion transfer device for insuring that the two crank arms forming partof the suspension means oscillate in unison so as to avoid tipping orlurching of the seat.

Another object is to provide a long life and low cost mounting for therubber torsion springs used as a part of the suspension means,particularly in providing an adequate journalling for the movable end ofeach rubber spring and to provide a thrust bearing arranged to resistthe tendency of the rubber torsion spring to elongate axially.

Other objects and advantages of the invention will be apparent from thefollowing description and drawings in which:

Fig. 1 is a side elevational View of a seat structure embodying thepresent invention and showing, in broken lines, a seat part including abucket seat, a base part in the form of a mounting plate, and asuspension means interposed between these parts.

Fig. 2 is a top plan elevation of the seat structure suspension meansshown in Fig. l.

Fig. 3 is a front elevational view thereof.

Fig. 4 is a fragmentary rear elevational view thereof.

Figs. 5, 6 and 7 are diagrammatic front elevational views of the seatingstructure embodying the present invention and showing the same indifferent positions, Fig. 5 showing, diagrammatically, the position ofthe parts when completely unloaded, Fig. 6 showing the position of theparts with the seat normally loadedA and Fig. 7 showing the position ofthe parts under an extreme bump or impact condition such as when thevehicle body is thrown violently upward on encountering an elevation inthe field.

Fig. 8 is an enlarged section taken generally on line 8 8, Fig. 4.

Fig. 9 is an enlarged section taken on line9-9, Fig. 2. v

Fig. l0 is a section taken on line itl-10, Fig. 9.

The vehicle seat structure embodying the present invention is designedprimarily for use where rough riding or extreme vertical and lateralimpact conditions are encountered, such as with the farm tractors,railroad locomotives and military vehicles, where lateral as well asvertical stability is required, and to this end the seat part 1li of theseat structure is shown as being in the form of a sheet metal buckettype of seat or saddle 11 carried through a hinge 12 by a seat support,which latter is suitably supported, as by bolts 14, to a supportingplate 15 which can be of any suitable contour. The end of the bucketseat 11 opposite its hinge 12 can be supported through a resilientcushion 16 on an extension 18 of the seat supporting plate 15. The partsas above described constitute the seat part 10 of the seat structure asused in the accompanying claims.

This seat part 10 is supported on a base part 20 of the seat structurethrough the spring suspension means embodying the present invention.While this base part can be of any form to suit the particularinstallation, it is shown as being in the form of a horizontal plate 21of generally triangular form in plan.

The spring suspension means of the present invention includes a pair ofupstanding flexible bodied connectors 25 mounted on the side extremitiesof the base plate 21.

As best shown in Figs. 2 and 3, each of these connectors 25 comprises anL-shaped metal spring leaf 26 reinforced by aV smaller L-shaped .metalbacking spring Vleaf 28.

These spring leaves of each connector have horizontal end parts whichare secured to the base plate 21 by rivets 29. Each spring leaf 26 alsohas a vertical part 3i) which projects upwardly and is arrangedore-and-aft with reference to the seat part 16 so that these upstandingparts 26 at opposite sides of the seat structure are freely tiexibletransversely of the seat structure. Such flexing is additionallyprovided by vertical upward extensions 31 of the backing spring leaf 28.The upper extremity of the vertical part 30 of each spring leaf 26 isbent into an open-ended cylinder or sleeve 32. These open-endedcylinders 32 are arranged at the same level parallel with each other andwith their axes extending fore-and-aft of the seat structure.

ln each of these open-ended cylinders or sleeves 32 is journalled thecrank pin 33 at the outer end of a corresponding crank arm 35. Eachcrank pin 33 is preferably formed by bending the end of the crank arm atright angles. As best shown in Fig. 9 each crank pin 33 is preferablyjournalled in a pair of bearing bushings 56, 36 tted in the oppositeends of the corresponding cylinder or sleeve 32. Each of these bearingbushings 36 is preferably made of sintered metal impregnated with alubricant so as to reduce service requirements.

Means are also provided for limiting the movement of the seat part 1i)of the seat structure, particularly for limiting the upward movement ofthis scat part as hereinafter described in detail.

For this purpose a stop pin 38 extends transversely through each of thecrank arm pins 33, 'and the ends of these pins project outwardly throughslots 39, 39 provided in the open-ended cylinders or sleeves 32. Theseslots are of such length, circumferentially ot' the cylinders or sleeves32, that their ends 40 engage the ends of the pins 38 at the end of apredetermined inward movement of the spring leaf parts 30 toward eachother to limit the upward movement of the bucket seat 1t) las shown inFig. 5. The downward movement of the` bucket seat can be limited bybottoming of the seat part plate on the base plate 21 as illustrated inFig. 7`

Each crank arm 3S has a fulcrum rod d2 to the center of which the crankarm is welded as best in Figs. 2 and 8. As best shown in Fig. 8, thefront end of each fulcrum rod 42 is journalled in a bearing bushing 43preferably of a lubricant impregnated sintered metal. This bearingbushing is press fitted into a thimble 44 pressed rearwardly from afront supporting plate 4S. Each bearing bushing 36 is backed by a pairof thrust washers 46, 43 which are held in operative position by a teator projection 49 squeezed out of the ulcrum rod 42 on the side of thewasher 4S remote from the corresponding bearing 43. The front supportingplate is shown as secured, as by welding, to a vertical part 50, of theforward end of the seat plate 15.

Each fulcrum rod 42 is journalled toward its rear end in a bearingbushing 51 preferably also made of lubricant impregnated sintered metal.Each bearing bushing 51 is press fitted into a thimble 52 pressedforwardly from a rear supporting plate 53. The iront side of eachbearing bushing engages a thrust washer 54 held in position by a teat orprojection 55 squeezed out of the fulcrum rod 42 on the side of thewasher 54 remote trom the corresponding bearing 51. The rear supportingplate is shown as secured, as by welding, to an integral vertical part56 of the rear end of the seat plate 15.

A cross pin 60 having projecting ends extends through the outboard endof each fulcrum rod 42 immediately in rear of the rear supporting plate53 and serves to hold this rear supporting plate 53 against rearwarddisplacement with reference to these fulcrum rods. Each of these crosspins 60 is also engaged by a thrust sleeve 61 which supports a thrustwasher 62 against the bearing bushing 63 of a rubber spring 65. Each ofthese rubber springs can be of any suitable construction and is shown ascomprising a generally truste-conical body 66 of rubber having -a fiatouter face 68 and a concave inner face 69.

To the outer iiat face 68 of each rubber body is vulcanized a metal disk70 having a hub 7i which fits the rear extremity of the correspondingulcrum rod 42 and can be secured thereto in any suitable manner as by across pin 73. To the opposite concave face 69 of each rubber body isvulcanized a conforming convex metal anchoring member or plate 75, thisanchoring plate having a cylindrical hub 76 in which the bearing bushing63 is press fitted. It will also be noted that this bearing bushing 63an outwardly extending ilange 78 against which the end of the hub '76bears, this ange 78 also serving to provide extended surface forrthethrust washer 62.

Each anchoring plate is also provided with an outwardly projectingmarginal flange 79. For protection, the corresponding outer edge of eachrubber body 66 is preferably in the form of an attenuated or featherediiange titi which extends outwardly along this flange 79 of theanchoring plate and is vulcanized thereto. The upper part of eachmarginal iiange 79 is extended upwardly to provide an ear 8i and topermit of the ready adjusting of both of the rubber springs 65 to havethe same initial degree of tension or windup, the anchoring plates 75 ofthese rubber springs are preferably adjustably interconnected. For thispurpose a swivel pin 82 is mounted in the upward extension 8l of themarginal flange 79 of each anchoring plate 75 of each rubber spring.Each swivel pin 82 oscillates about a horizontal axis parallel with thecorresponding fulcrum rod 42. Each of these swivel pins S2 has a greatlyenlarged head 33 disposed against the outer face of the ear 81 and alsohas a round shank 84 extending through a round opening S5 in thecorresponding extension 81 of the anchoring plate 75. The swivel pins 82are retained in position by drive pins 86, 86o and it is a feature ofthe invention that at least the drive pin 86a is of suicient length toprovide a pointer traversing a scale as hereinafter described.

The enlarged head of each swivel pin 82 is provided with a transversethreaded opening 8S in which is screwed a threaded adjusting rod S9which extends transversely of the seat structure. The threads 9i) at oneend of this adjusting rod S9 and threadedly engaging the correspondingswivel pin head 33 are pitched in the opposite direction from thethreads 91 on the opposite end of this adjusting rod. One end of thisadjusting rod is provided with a transverse handle 92 which isconveniently accessible to the occupant of the seat structure foradjusting the degree of tension or windup of the springs.

A feature of the seat resides in the provision of a calibrated scale bywhich the scat can readily be adjusted to have a degree of pretension orwindup corresponding to the weight of the driver.

For this purpose a thin metal plate 95 is interposed between the rearextremity of the seat supporting plate 15 and the supporting member 13for the bucket seat 11. This plate is traversed by the drive pin 86a forone of the swivel pins 82, this drive pin being preferably extendedupwardly an abnormal distance as compared with the other drive pin 86 soas to provide a pointer traversing the scale 96 provided on the plate95. The scale can be calibrated in different weights of the drivers sothat a driver knowing his own weight can turn the screw 89 until the pin86a is in register with his particular weight. The seat then has theproper degree of windup or pretension to properly support his weight.

To prevent sidewise tipping or lurching of the seat part 10, the twofulcrum rods 42 are interconnected so as to rotate in unison. Theconnection between these two fulcrum rods is shown as being in the formof a link 98 pivotally connected at its opposite ends to the metal disks70 of the two rubber springs 65. For this purpose each of these metaldisks 70 has mounted therein a pin 99 the stem 100 of which projectsrearwardly and the head 101 of which is embedded in the rubber body 66as best shown in Fig. 8. The link 98 has an oversize opening at each endthrough which the stem 100 of a pin 99 extends and a bearing bushing 102of lubricant impregnated sintered metal is preferably press tted in eachof these oversize openings so as to provide a bearing bushing for thecorresponding shank 100 of the pin 99. Each end of the link 98 ispreferably anked by a washer 103 and a cotter pin 104 or the like servesto hold these washers and the link on the shanks 100 of the pins 99.

Assuming the normal loaded position of the Seat structure illustrated inFig. 5, in the operation of the suspension, the upward movement of thetractor, through the base plate 21 and spring leaf connectors 25 movesthe outer or free ends of the crank arms 35 upwardly, these outer orfree ends being formed to provide the integral crank pins 33 which arejournalled in the cylindrical sleeves 32 formed at the upper end of thespring leaf connectors 25. The fulcrum rods 42 of these crank arms 35oscillate about their bearings 43 and 51. These bearings 43 and 51 aresecured in the thimbles 44 and 52 of the front and rear plates 45 and 53which form a part of the seat part of the seat structure and support thebucket seat 11.

The oscillation of each crank arm 35 is resisted by the correspondingrubber spring 65, this movement of each of these crank arms 35 beingtransmitted through the pins 73 to the disk 70 vulcanized to the at rearend face 68 of the rubber body 66 of each rubber spring. The forward endof each rubber body 66 is vulcanized to the convex anchoring plate 75,and hence the force so imposed on the rubber body is transmitted to theupwardly extending ears 81 of these convex metal anchoring plates 75.These two ears S1 are adjustably connected together by their swivel pinsS2 and the reversely threaded screw 89 and hence it will be seen thatthese connected ears 81 provide a nonrotating anchorage for the forwardends of the rubber springs. When it is desired -to increase the initialtension or windup of the springs the reversely threaded rod 89 isturned, through its handle 92, in a corresponding direction. In soturning, the upward extension of the drive pin 86a for the correspondingswivel pin 82 is caused to traverse the graduations 96 on the plate 95.These graduations are calibrated in accordance with the weights ofdifferent drivers. Accordingly, the driver can preadjust the seat to hisown Weight by turning the handle 92 until the pointer formed by theupward extension of the drive pin 86a registers approximately with hisweight. This adjustment is preferably made before he sits upon the seatstructure although this adjustment can be made, of course, while thedriver is seated upon the seat structure. The position of the partsfollowing a violent upward impact from the tractor isillustrated in Fig.7.

Lateral tipping of the bucket seat 11 is prevented by the link 98interconnecting the end plates 70 of the two rubber springs 65. Thislink pivotally connects the disks 70 of these two rubber springs torotate in unison and since these plates 70 are xed to the two fulcrumrods 42 by the pins 73, this link compels the two fulcrum rods 42 andtheir crank arms 35 to oscillate in unison. It Will be noted that by thepositioning of the link 98 as shown, the swinging movement of one crankarm can only occur when there is a corresponding. movement of the othercrank arm. At the same time, the bucket seat or saddle 11 is capable oflateral movement and this movement is yieldingly permitted by -theexible bodied spring leaves which support the outer or crank pin ends 33of the crank arms 35. It will also be particularly noted that theseflexible bodied spring leaf connectors have the ability to accommodatethe spreading and contracting of the outer or crank pin ends 33 of thecrank arms as the seat part of the seat structure falls and rises. Thisrelative movement of these crank pins 33 with reference to each other isindicated by the vertical dot-dash line in Fig. 5. At the same time theuse of these flexible bodied connectors 25 yieldingly holds the seatpart of the seat lstructure in centered relation tothe base part. Thisis an important feature since if shackles were substituted for theilexible bodied connectors, it will be seen that these shackles wouldmerely flop over to one side or the other so that the suspension wouldbecome inoperative.

When the seat part 10 is so forced downwardly relative to the base partor base plate 20 from the normal loaded position shown in Fig. 6,or,-conversely, when the base part 10 is forced upwardly relative to theseat part 20, the eifective opposing force of the rubber springsincreases at ageometric and not at an arithmetic rate. In thisparticular case the geometric rate of change of resilient resistance isof the accelerated increase type in which increments of verticalmovement of the base part are opposed by an accelerated rate of increaseof resilient resistance. This is due to the progressive decrease in theeiective leverage of the crank arms 35 as they swing downwardly andoutwardly from the position shown in Fig. 6 to the position shown inFig. 7 about their fulcrum rod axes of rotation. This action is alsoinfluenced by the fact that increments of vertical displacement of theouter ends of the crank arms cause accelerated rates of increase in theangular displacement of the rubber torsion springs 65. This latter isdue to the fact that increments of vertical movement of the outer endsof the crank arms 35 are not proportional to the accompanying incrementsof angular twist to which the rubber springs are subjected.

This geometric action also occurs when the base part 20 moves downwardlyrelative to the seat part 10 from the position shown in Fig. 6 to theposition shown in Fig. 5. Throughout this particular movement thegeometric action is of the accelerated decrease type, that is,

-as the base part 2i) passes through increments of downward movement therate of decrease of the resilient force tending to push the seat partdownwardly increases.

By this means, so far as vertical forces are concerned, the seat part l0is free to float along solely under the influence of gravity (pluswhatever vertical momentum forces Aare present) this feature being ofparticular significance when it is realized that the occupant is also,at this time, solely under the influence of gravity (plus whateververtical momentum forces are present). The consequence is that withinthis particular range of movement the occupant of the seat movesvertically up and down with the same acceleration and deceleration asthe seat part 10 and hence without changing the pressure between theoccupant and the seat. Such a ldesirable result is quite .different fromthat obtained from conventional seat suspension means in which thevertical drags jerks the seat down whenever the strains imposed on theseat part are negative. With the present seat suspension means no suchforces tending to pull the seat downwardly are possible.

It will particularly be noted that by arranging the flexible bodiedsupports 25 at the side of the base plate 21 and with their broad facesextending fore-and-aft, a high degree of lateral cushioning orresiliency is imparted to the seat part 10 while at the same time theseflexible bodied supports always tend to center the seat part 10, and -donot permit such amplitude of movement as would interfere with the driverreaching his controls.

Further, the maximum elevation of the seat part 10 is determined by thesimple expedient of the pins working in the slots 39 of the sleeves 32.The corresponding ends of these slots determine the degree ofoscillation of the crank pins 33 in the directions which they mustrotate as the seat part rises and hence determine the elevation to whichthis seat part can rise. These stops therefore are factors indetermining the pretensioning or windup of the rubber torsion springs65. As the handled screw 89 is turned to spread the ears 81 of theanchoring plates 75 of the two rubber springs 65, the rubber bodies 66thereof tare stressed to raise the seat part 10. With such raisingstopped by the pins 38 engaging the shoulders 40 provided bythe slots39, furtherV turning of the handledv screw S9 serves to pretension therubber bodies 66. A feature off the invention is the simpleV provisionofY a pointer and scale calibrated in terms ofj driverweights. Thepointer is provided by an extension of one of' the drive pins 86a forone of the swivel pins 82 carrying the handled screw 89; The drivermerely sets this pointer to his approximate weight on the calibratedscale 96V and he is assured a good ride.

It will also be seen that features of the invention are the simple link98 connecting the plates 70 and hence the fulcrum rods 42 to oscillatein unison and which hence eliminates lurching of the seat part; thesimple bearing 63, 76 for the anchoring plate 69 of each rubber spring;the simple thrust bearing 78, 62, 61 and 60 for each of thesel lastbearings to overcome ther natural tendency of the rubbery springs 65 toelongate axially; and the use of this' same pair of stops 60 as thethrust abutments for the bearings 5.1'.

We claim:

l'. A seat structure, comprising a seat part, a base part, a pair ofgenerally horizontal, generally parallel spaced fulcrum rods joui-nailedin one of said parts, at least one normally generally horizontalk crankarm fixed to each` of said fulcrurn rods and projecting toward the otherof said parts, a movable member pivotally connecting 4the free end ofeach of said crank -arms with the other of said parts, transverse platesseverally fixed to said fulcrum rods 4and arranged substantially in a.common plane extending perpendicularly to said ful'crum rods, a rubberbody fixed at one end to one face of each of said transverse plates, ananchoring plate ixed to the opposite end of each of said rubber bodies,means interconnecting said anchoring plates to restrain rotationthereof, and means compelling said ulcrumrods to rotate in unison,comprising a link pivoted to each of said. transverse plates andcompelling said transverse plates to rotate in unison.

2. A seat structure as set forth in claim l wherein the pivotalconnection between each of said transverse plates and. said linkincludes a pivot pin having a head embedded in the corresponding rubberbody and a shank projecting through openings in the correspondingtransverse plate and in the adjacent end of said link.

3. A seat structure, comprising a seat part, a base part, a pair ofVgenerally horizontal, generally parallel spaced fulcrum rods journalledin one of said parts, at least one normally generally horizontal crankarm fixed to each of said fulcrum rods land projecting toward the otherof said parts, a movable member pivotally connecting the free endof eachof said' crank arms with the other of said parts, transverse platesseverally xed to sai-d fulcrum rods and arranged substantially in acommon plane extending` perpendicularly to said fulcrum rods, a rubberbody fixed at one end to one face of each of said transverse plates, ananchoring plate `lixed to the opposite end of each of said rubberbodies, a swivel pin rotatably secured to the marginal part of each ofsaid anchoring plates to rotate about an axis parallel with said fulcrumrods, each of said swivel pins including an enlarged head provided witha threaded bore alining with the threaded bore of the other swivel pinhead, an adjusting rod having reversely threaded ends severally screwedinto said threaded bores, a pointer carried by one or" said anchoringplates, and a plate carried by said one of said parts and having acalibrated scale traversed by said pointer.

4. A seatstructureas set forth in claim- 3 wherein said pointer`comprisesone end of a pin securing one of saidswivel;pinsagain'st-axialy displacement.

5-. A seat structure, comprising a seat part, a base part, apair ofigenerally horizontal, generally parallel spaced ulcrum rods jour-nailed`in one of said parts, at least one normally generallyV horizontal crankarm fixed to each of said fulcrum rods and projecting toward the otherof said parts, amovable member pivotally connecting the free end of eachof said crankv arms with the other of said parts, transverse platesseverally fixed to said fulcrum rods andv arranged' substantially in acommon plane extending perpendicularlyY to said fulcrum rods, a rubberbody fixed at one end'to one face of each of said transverse plates, ananchoring-plate fixed to the opposite endY of each of said' rubberbodies, each of saidy anchoring plates being provided with anl integraltubular' hub surrounding the corresponding fulcrum rod, a bearingbushing press fitted in each of'said hubs and rotatable on the peripheryof the corresponding fulcrum rod, and means restraining rotation of saidanchoring plates.

6. A seat structure as set forth in claim 5 wherein each bearing bushinghas a radially outwardly projecting ange engaging the end of its hubopposite the corresponding rubber body, andy wherein the side of eachiiange opposite its hub is engaged by a thrust washer held againstdisplacement along its fulcrum rod by a radial projection from saidfulcrum rod;

7. A seat Structure as set forth in claim 6 wherein a thrust sleeve isinterposed between each of said thrust washers and' the correspondingradial' projection.

8. A seat structure as set forth in. claim 6 wherein said radialYprojections also severally serve as thrust abutments for the bearingsjournalling said fulcrum rods in said one of said parts.

9. A seat structure comprising a seat part, a base plate, a pair ofgenerally horizontal closely spaced fulcrum rods journalled in said seatpart to swingyabout horizontal axes extending fore-and-aft of the seatstructure, a crank arm xed to each of said fulcrum rods and projectinghorizontally outwardly therefrom'in the normal loadedl condition of theseat structure, a crank pin at the free end of each crank arm andextending generally parallel with said fulcrurn rods, an L-shaped springleaf having a base part attached to said base plate and having its upperend formed to provide a cylindrical' open-endedsleeve in which acorresponding crank pin is journalled, said L-shaped spring leaves beingcapable of flexure in a horizontal direction toward' the fore-and-aftcenter of the seat structure, a transverse pin projecting from each ofsaid crank pins through a slot in the corresponding open-ended sleeve,said slots being of such length that the ends thereof serve as stopshoulders for said transverse pin thereby to limit the upward movementof said seat part, relative to said base plate, and meansyieldinglyresisting vertical movement of said seat part relative to said baseplate.

References Cited in the. file of this patent UNITED STATES PATENTS2,156,507

